Whats the right way to create scenes ready for gltf and draco compression?
Ok i got it. It is indeed a bug in the glTF-Blender-IO addon. See https://github.com/KhronosGroup/glTF-Blender-IO/issues/993. There is also a workaround described how we can solve this. So what stays is the hope that other people will find this solution a bit earlier than me and there will be a bugfix soon...